3.从尾到头打印链表

题目描述

输入一个链表，按链表从尾到头的顺序返回一个ArrayList

方法一：

翻转链表,然后重新遍历放入到数组中;

 public ArrayList<Integer> printListFromTailToHead(ListNode listNode) {
        ListNode pre = null, now = listNode, next = listNode;
        //1->2->3->4
        while (now != null) {
            next = now.next;
            now.next = pre;
            pre = now;
            now = next;
        }
        ArrayList<Integer> arrayList = new ArrayList<>();
        while (pre != null) {
            arrayList.add(pre.val);
            pre = pre.next;
        }
        return arrayList;
    }

方法二：

依次遍历放入栈中,然后遍历栈

import java.util.ArrayList;
import java.util.List;
import java.util.Stack;
import java.util.ArrayList;
public class Solution {
    // 
    public ArrayList<Integer> printListFromTailToHead(ListNode listNode) {
        Stack<Integer> stack = new Stack<>();
        while (listNode != null) {
            stack.push(listNode.val);
            listNode = listNode.next;
        }
        ArrayList arr = new ArrayList();
        while (!stack.isEmpty()) {
            arr.add(stack.pop());
        }
        return arr;
    }
}

方法三：

递归